Full Idea
Deontic accessibility seems not to be reflexive (that it ought to be true doesn't make it true). One could argue that it is serial (that there is always a world where something is acceptable).
Gist of Idea
Intuitively, deontic accessibility seems not to be reflexive, but to be serial
Source
Theodore Sider (Logic for Philosophy [2010], 6.3.1)
Book Reference
Sider,Theodore: 'Logic for Philosophy' [OUP 2010], p.142